Question

The number of species below that have two lone pairs of electrons in their central atom is _____. (Round off to the Nearest Integer).

SF$_{4}$, BF$_{4}^{-}$, ClF$_{3}$, AsF$_{3}$, PCl$_{5}$, XeF$_{4}$, SF$_{6}$

Answer 1

2

Answer 2

To determine the number of species with two lone pairs of electrons on their central atom, we will analyze each given species using the VSEPR theory and calculate the number of lone pairs.

The number of lone pairs (LP) on the central atom can be calculated as:

$\text{LP} = \frac{(\text{Valence electrons of central atom} + \text{electrons from negative charge} - \text{electrons used in bonding}) }{ 2}$

Let's analyze each species:

1. SF₄:

   • Central atom: S (Sulfur)
   • Valence electrons of S = 6
   • Number of F atoms bonded = 4 (each forms a single bond, so 4 electrons used)
   • Remaining electrons = 6 - 4 = 2 electrons
   • Number of lone pairs = 2 / 2 = 1
   • Conclusion: SF₄ has 1 lone pair.

2. BF₄⁻:

   • Central atom: B (Boron)
   • Valence electrons of B = 3
   • Negative charge = 1 (adds 1 electron)
   • Total electrons for bonding/lone pairs = 3 + 1 = 4
   • Number of F atoms bonded = 4 (4 electrons used)
   • Remaining electrons = 4 - 4 = 0 electrons
   • Number of lone pairs = 0 / 2 = 0
   • Conclusion: BF₄⁻ has 0 lone pairs.

3. ClF₃:

   • Central atom: Cl (Chlorine)
   • Valence electrons of Cl = 7
   • Number of F atoms bonded = 3 (3 electrons used)
   • Remaining electrons = 7 - 3 = 4 electrons
   • Number of lone pairs = 4 / 2 = 2
   • Conclusion: ClF₃ has 2 lone pairs. (This one counts)

4. AsF₃:

   • Central atom: As (Arsenic)
   • Valence electrons of As = 5
   • Number of F atoms bonded = 3 (3 electrons used)
   • Remaining electrons = 5 - 3 = 2 electrons
   • Number of lone pairs = 2 / 2 = 1
   • Conclusion: AsF₃ has 1 lone pair.

5. PCl₅:

   • Central atom: P (Phosphorus)
   • Valence electrons of P = 5
   • Number of Cl atoms bonded = 5 (5 electrons used)
   • Remaining electrons = 5 - 5 = 0 electrons
   • Number of lone pairs = 0 / 2 = 0
   • Conclusion: PCl₅ has 0 lone pairs.

6. XeF₄:

   • Central atom: Xe (Xenon)
   • Valence electrons of Xe = 8
   • Number of F atoms bonded = 4 (4 electrons used)
   • Remaining electrons = 8 - 4 = 4 electrons
   • Number of lone pairs = 4 / 2 = 2
   • Conclusion: XeF₄ has 2 lone pairs. (This one counts)

7. SF₆:

   • Central atom: S (Sulfur)
   • Valence electrons of S = 6
   • Number of F atoms bonded = 6 (6 electrons used)
   • Remaining electrons = 6 - 6 = 0 electrons
   • Number of lone pairs = 0 / 2 = 0
   • Conclusion: SF₆ has 0 lone pairs.

The species that have two lone pairs of electrons in their central atom are ClF₃ and XeF₄. Therefore, there are 2 such species.